This invention relates to rotary motion transmitting devices and more particularly, to friction drive transmissions which transmit rotational power in a speed changing manner through the use of a plurality of cylindrical rolles arranged in a planetary configuration.
Planetary gear systems are well known in which a plurality of pinions travel around the circumference of a sun gear and engage an internal ring gear. Such systems are compact and have input and output shafts which are axially aligned. In addition, the side pressure of the input and output shafts is equalized. However, the expense of machining planetary gear systems frequently prevents their use.
In order to develop an economical alternative to planetery gear systems, several planetary drive systems utilizing ball bearings or cylindrical rollers have been designed. Such systems have employed various techniques to insure that sufficient frictional contact is maintained between the rolling elements. U.S. Pat. No. 3,793,907, issued Feb. 26, 1974, to Nakamura et al. discloses a frictional drive system which utilizes hydraulic pressure to control the frictional contact between rolling elements. U.S. Pat. No. 3,817,125, issued June 18, 1974, to Nakamura et al. utilizes elastically deformed planetary rollers. U.S. Pat. No. 3,776,051, issued Dec. 4, 1973, to Kraus and U.S. Pat. No. 3,945,270, issued Mar. 23, 1976 to Nelson et al. both utilize drive systems in which the shafts are on axes which are parallel to but slightly spaced from each other. This provides a varying annular space between one shaft and a traction ring attached to a second shaft. A plurality of drive rollers which are disposed between the first shaft and the traction ring are provided with certain degrees of freedom so that they can be wedged between the shaft and the traction ring. The present invention utilizes a pinch roller planetary design which avoids the expense of machined gears while providing for equalized side pressure on axially aligned input and output shafts. In addition, this invention does not require a constant pressure on the rollers to obtain the traction needed to prevent slippage. The necessary pressure is supplied in response to the torque required, utilizing a pinch principle.
A typical pinch roller drive system, such as found on a phonograph turntable, includes a pinch roller which is loosely held against a motor shaft and the rim of a cylinder being driven. A drive force causes the roller to pinch between the motor shaft and the cylinder. This pinching action is a function of the drive pressure. Therefore, the pressure of the drive is directly proportional to the load requirement. When the load is great, the roller pressure is great. When the load is light, there is little pressure on the rollers. This automatic pressure loading results in an efficient, dependable, quiet and long-lasting drive system.